Glass for television display cathode-ray tubes

ABSTRACT

Glass for envelopes of television display cathode-ray tubes, particularly screen glass for color television, which transmits at most 0.5 mr/h of X-ray radiation at an acceleration voltage of 40 to 45 k. volt, and which has a composition in percent by weight: SiO2 58-67 PbO 2-7 Li2O 0-1 MgO 0-3 Na2O 2-3 Al2O3 14 K2O 11-14 As2O3 + OR - 0.3-0.7 Sb2O3CaO 3-4.5 CeO2 0.05-0.6 BaO 11-14

O Elmted States Patent 1151 8,668,246

La Grouw 1 May 16, 11972 [54] GLASS FOR TELEVISION DISPLAY FOREIGN PATENTS 0R APPLICATIONS CATHODE-RAY TUBES 1,123,857 8/1968 Great Britain 106/53 [72] Inventor: Coenraad Maria La Grouw, Emmasingel, 1

Eindhoven Netherlands Prrr nary Examiner-James E. Poer Assistant Exammer--M. Bell [73] Assignee: U.S. Philips Corporation, New York, NY. Attorney-Frank R. Trifari [22] Filed: Oct. 22, 1969 [57] ABSTRACT [2]] Appl' 8686" Glass for envelopes of television display cathode-ray tubes, particularly screen glass for color television, which transmits [30] Foreign Application Priority Data at most 0.5 mr/h of X-ray radiation at an acceleration voltage 0m. 28, 1968 Netherlands ..6815397 of i f 45 and whch has a mp0smon percent by weight.

[52] U.S. Cl ..106/53 s c 5g 7 p o 7 [51] Int. Cl. ..C03c 3/04, C03c 3/10, H011 29/10 U 0 0.1 Mg@ [58] Field ofSearch. 106/53;3l3/89;252/301 4 F o 2 3 1 0 1 4 K 0 1114 AS303 i Sb O 0 3-0.7 [56] References Cited C o 3 4 5 0 0 05 6 UNITED STATES PATENTS B30 1 2,856,303 10/1958 Armistead ..106/53 3,422,298 1/1969 De Gier ..106/53 2 Claims, N0 Drawings GLASS FOR TELEVISION DISPLAY CATIIODE-RAY TUBES The invention relates to glass for an envelope of a television display cathode-ray tube, particularly glass for the face-plate of the tube.

Particular requirements are imposed on glass for envelopes of cathode-ray tubes for the display of colored television images as compared with that for the display of monochrome television images. Such special glasses are known, for example, from the British Pat. specification No. 1,123,857 the composition of which in percent by weight lies within the following range of compositions:

s10, 62-66 B210 1 1-14 up -1 MgO 0-3 Na,0 7-s.s PbO 0-2 x,o 6.59 A120, 14 C210 2 4.5 As,0,+

sb,o 0.3-0.7 ceo 005-03 The special requirements which, as compared with glass for the envelopes for monochrome display, are imposed on glass for envelopes for color display, are connected with differences in the manufacture and in the use of these tubes. In the first place, the glass components of envelopes for color display unlike those for the monochrome display envelopes cannot be sealed by fusing them together but must be connected together with the aid of an enamel. This is connected with the fact that a shadow mask is provided in these tubes, which mask determines the path of the required three electron beams. Furthermore, an extremely fine grating-like pattern of three different luminescent substances corresponding to the apertures of the shadow mask is provided on the inner side of the screen. The requirements relative to the maximum permissible distortion of the glass are in this case much more stringent in connection therewith than for glass of envelopes for monochrome display. In addition, the temperature at which the tube must be heated during evacuation and sealing must be approximately 20 higher and the heat treatment is of a longer duration than for the tubes for monochrome display.

The glasses within the above-mentioned range are eminently satisfactory in a technological respect relative to the softening point, the quality and the thermal coefficient of expansion. For the acceleration voltages until recently used on the electron guns, the absorption of these glasses for the X-ray radiation generated during operation as a result of the electron bombardment on the glass and on the shadow mask is sufficiently great. This even applies when the tube is built in in a cabinet in direct vision construction, thus without a protective cover glass.

The requirement up till now had been that the intensity of the transmitted X-ray radiation may be at most 0.5 milliroentgen per hour (mr/h) at a maximum thickness of l 1 mm of the screen glass, an acceleration voltage of 27.5 k. volt and an anode current of 300 [.LA in a television display tube.

There is, however, a tendency to still further increase the margin of safety to X-ray radiation transmitted by television display tubes. There is a need of a kind of glass in which at most 0.5 mr/h is transmitted at an acceleration voltage of 35 k.voltv The above-described glasses then no longer have a sufficiently high absorption and do not satisfy the stricter safety requirements. For reasons of a technological nature, the thickness of the screen cannot be increased much further than I 1 mm. To obtain a sufficiently high absorption while using a glass within the above-mentioned range of compositions, the screen should be thicker by as much as 2.5 mm.

For a satisfactory processing of the glass and moulding faceplates thereof, it is necessary that the temperature dependence of the viscosity is not too great. In practice this means that the temperature difference between the softening point, which is the temperature at which the viscosity of the glass is poises, and the annealing point, which is the temperature at which the viscosity of the glass is 10 poises, must be at least 190 C.

In connection with the conventional manufacturing technique and the very stringent requirements which are imposed on the maximum permissible distortion of the glass components during manufacture of the tube, it is necessary that glass for a color display tube has an annealing point which is not lower than 485 C.

Finally it is of importance that a glass for a color television display tube has approximately the same coefficient of expansion as that of the known glasses (approximately 99 X 10" between 30 and 300 C.), so that a better match is obtained with the existing glasses and metal components which must be sealed on or in respectively.

In the kind of glass according to the present invention, a content of PbO is present with an approximately equal BaO content relative to the known glass. It is by no means surprising in itself that the absorption of X-ray radiation is increased as a result thereof. It was, however, not obvious that it was possible to maintain the physical properties of the glass at the same level by means of a few other modifications. Furthermore, it is also known (from U. K. Pat. specification No. 664,769) that no discoloration occurs on the glass of the faceplate due to electron bombardment, provided that the glass contains Ce0 and provided that the glass contains no more than 1 percent of readily reducible oxides. However, the glass according to the invention which does not satisfy the last-mentioned requirement owing to its content of PbO, does not discolor under the influence of the electron bombardment.

The range of glass compositions according to the present invention is characterized by the following limits in percent by weight:

sio 58-67 PbO 2-7 1.1,0 0-1 MgO 3 Na O 24 A1 0, 14 K20 1 1-14 As O 0.3-0.7 CaO 34.5 CeO, 0.05-0.6 BaO 1 1-14 The softening point of these glasses lies between 690 and 710 C.; the annealing point between 485 and 510 C. and the thermal coefficient of expansion is approximately 97 to 100 X 10 between 30 and 300 C. The glasses according to the invention amply satisfy the above-mentioned requirement of transmitting at most 0.5 mr/h at an acceleration voltage of 35 K.volt; it was found that this amount was not yet reached at an acceleration voltage of even 44 to 45 k.volt when using these glasses. The electric resistance thereof is at least 10" ohm. cm and at least 10 ohm.cm at 250 and 350, respectively, while these values are 10* and 10' ohm.cm for the abovementioned known glasses.

The following glass is an example of a glass suitable for the relevant purpose. It is obtained in a manner which is common practice in glass technology by melting the relevant oxides or compounds which are converted into the oxides.

SiO, 59% by weight PbO 6.3% by weight. Li O 0.4% by weight A1 0 2.2% by weight. Na o 2.4% by weight Sb O 0.3% by weight. K 0 12.7% by weight CeO 0.5% by weight. CaO 3.6% by weight Softening point 705C. BaO 12.3% by weight annealing point 502C.

coefiicient of expansion (30300 C.) 97 X 10' logp250C. 10.3 logp 350C. 8.2.

What is claimed is:

1. Glass for envelopes of television display cathode-ray tubes, particularly intended for the face-plate of the tube, consisting essentially of the following in percent by weight:

sio 58-67 PbO 2-7 up O-l MgO 0-3 Na O 2-3 A1203 1-4 14.0 11-14 As O 0.3-0.7

sb o

BaO 11-14 sio 59 up 0.4 N3 0 2.4 K20 12.7 CaO 3.6

BaO 12.3 PbO 6.3 A: 22 sb,o, 0.3 CeO, 0.5

mg? UNITED STATES PATENT OFFICE CERTIFICATE OF QOREQTIUN Patent No.3 563.246 Dated May 16, l972 In t COENRAAD MARIA LA GROUW It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Index, under [30] Foreign Application Priority Data" the priority date should read Oct. 29, 1968 Column 2, line 35, "AS 0 should read AS203 $13 0 In Claim 1, on the line befor "BaO 11-14' insert the following:

- CaO 3 4.5 Ce0 0.05 0.6

Signed and sealed "this 1st day of May 1973.

(SEAL) Attest:

M. FLETCHER, ROBERT GOTTSCHALK .attesilng Officer Commissioner of Patents Signed and sealed this day of 1 1972.

gggg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3 3 24 Dated May 16, 1972 In t COENRAAD MARIA LA GROUW It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected .as shown below:

In the Index, under [30] Foreign Application Priority Data" the priority date should read Oct. 2-9, 1968 Column 2, line 35, "AS 0 should read AS203 $13 0 In Claim 1, on the line befor "BaO ll-'l4" insert the following:

CaO 3 4.5 CeO 0. O5 0.6

Signed and sealed this 1st day of May 1973.

(SEAL) Attest':

M. FLETCHER, JR. ROBERT GOTTSCHALK' attesting Officer a Commissioner of Patents Signed and sealed this day of 

2. Glass as claimed in claim 1, consisting essentially of the following in percent by weight: SiO2 59 BaO 12.3 Li2O 0.4 PbO 6.3 Na2O 2.4 Al2O3 2.2 K2O 12.7 Sb2O3 0.3 CaO 3.6 CeO2 0.5 